The invention relates to new propellant gases which contain as a typical ingredient 1,1,1,2,3,3,3-heptafluoropropane (TG 227), the use of these propellant gases in pharmaceutical preparations suitable for producing aerosols, and these pharmaceutical preparations themselves.
Aerosols of powdered (micronised) drugs are used widely in therapy, e.g., in the treatment of obstructive diseases of the respiratory tract. If such aerosols are not produced by atomizing the pharmaceutical powder or by spraying solutions, suspensions of the drugs in liquefied propellant gases are used. The latter consist primarily of mixtures of TG 11 (trichlorofluoromethane), TG 12 (dichlorodifluoromethane) and TG 114 (1,2-dichloro-1,1,2,2-tetrafluoroethane), optionally with the addition of lower alkanes such as butane or pentane, or with the addition of DME (dimethylether). Mixtures of this kind are known for example from German Patent 1178975.
Owing to their harmful effect on the earth""s atmosphere (destruction of the ozone layer, Greenhouse effect) the use of chlorofluorocarbons has become a problem, with the result that the search is on for other propellant gases or propellant gas mixtures which do not have the above-mentioned harmful effects or, at least, have them to a lesser degree.
However, this search has come up against major problems, since propellant gases for therapeutical use have to satisfy numerous criteria which cannot easily be reconciled, e.g., in terms of toxicity, stability, vapor pressure, density and solubility characteristics.